Dr. Chaojun Ma Profile

Dr. Chaojun Ma

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Proceedings Article | 4 March 2024 Paper

Research on secondary signal acquisition system for instrument transformers based on time synchronization technology

Zemin Qu, Chen Hu, Yongzheng Zhu, Chaojun Ma, Yang Jiao

Proceedings Volume 12981, 129811X (2024) https://doi.org/10.1117/12.3014761

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To realize the online monitoring and condition assessment of transformers in a substation, synchronous acquisition of the secondary signals from multiple interval transformers across the entire station is required. A signal acquisition system has been designed, consisting of a time synchronization unit, a signal conditioning unit, a data acquisition unit, and a host computer. The time synchronization unit synchronizes the secondary signals from multiple interval transformers. The signal conditioning unit converts the output signals from the transformers into low-voltage signals. The data acquisition unit controls the sampling timing of the analog-to-digital converter (ADC) using FPGA and reduces phase errors through a time-digital-converter-based ADC sampling delay compensation method. The host computer employs the FFT algorithm with a fourth-order Blackman-Harris window to calculate the amplitude and initial phase of the secondary signals. The test results demonstrate that the system's error meets the requirement of a 0.05-class accuracy. The measurement errors between different channels and different data acquisition units are all less than 0.05%

Proceedings Article | 16 December 2022 Paper

Energization-status identification method of three-core cables based on annular magnetic sensor array

Yingying Xu, Hongbin Li, Qing Chen, Chaojun Ma, Yifan Gu, Linshan Han

Proceedings Volume 12500, 125003H (2022) https://doi.org/10.1117/12.2660830

KEYWORDS: Magnetism, Magnetic sensors, Finite element methods, Inverse problems, Reconstruction algorithms, Error analysis, Safety, Power supplies

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As three-core power cables are increasingly used in power distribution networks, the maintenance and overhaul of cable status have been paid more and more attention to. Because of the high risk of construction operations on energized cables, the energization-status identification of cables not only ensures the reliability of power supply in the power system, but also is a strong guarantee for the safety of repair crew. Recently, research has been carried out on energization-status identification of power cables, but the accuracy of identification results cannot be fully guaranteed. In this paper, we propose an energization-status identification method of three-core cables based on annular magnetic sensor array. According to the parameters of cable, an analytical model of surface magnetic field for three-core cable is constructed, which is used to determine the analytical function of inverse problem about the phase currents and magnetic field around the cable. Combined with the position of measurement points, the measured circumferential magnetic field amplitudes are interpolated. The inverse problem is transformed into a multi-objective optimization problem, and the IMODE algorithm is used to reconstruct the phase currents from the measured values to determine the energization-status of cable. In addition, the proposed method is still effective for the cables with three-core arbitrary distribution. Furthermore, an experiment for the energization-status identification of a three-core cable under low-current was carried out in the laboratory to verify the effectiveness of proposed method.

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